Phase synchronization systems for controlling the phase relationship between two signals are disclosed in the prior art and have been adapted for use in those technologies requiring velocity control of a first moveable member in accordance with the velocity of a second moveable member. For example, in copending application Ser. No. 89,869 filed Nov. 16, 1970, an assigned to the assignee of the present invention, a phase synchronization system is disclosed wherein, in a preferred embodiment, the first moveable member comprises a filmstrip and the second moveable member comprises a web having a preprinted format thereon, such as headings, columns and the like. Since the filmstrip and web, when operative, are both continuously moving, phase synchronization therebetween is required such that the information prerecorded on the filmstrip is accurately printed at the appropriate portion of the web. The phase relationship between the signals representing the velocity of the filmstrip and the web is determined by a comparator which produces a pulse width modulated signal indicative of the phase relationship. The pulse width modulated signal is applied to an integrator and thence to a storage means, the output of the storage means being of an amplitude representing the phase error between the aforementioned velocity signals. The output of the storage means is coupled to a control voltage generator, the output thereof causing a motor to adjust the velocity of the first filmstrip such that phase synchronism is attained.
At start-up (when the apparatus incorporating the phase synchronization system described hereinabove is initially operative), the determined phase error may range from a relatively insignificant error to the maximum error possible, i.e., the situation wherein the pulse signal representing the velocity of the member not being controlled is substantially in phase with the second pulse in the pulse sequence representing the velocity of the member being controlled. In the latter situation, the time necessary to attain a predetermined phase relationship becomes a significant factor in decreasing the efficiency and speed of the system operation. Further, during normal operation of the system, the measured phase error may be greater than allowed by system requirements (i.e., the information would be printed in the wrong column). Therefore, it would be desirable to incorporate in the type of system described hereinabove a technique wherein the phase error, at start-up, is rapidly reduced to a predetermined level, the phase error continually being monitored such that the system is shut down if the phase error exceeds said predetermined level.